Ndc1 catches the shuttle

The protein Ndc1 commutes between jobs in yeast cells. Chen et al. pinpoint a nuclear membrane protein that might give it a ride.

In budding yeast, Ndc1 helps insert nuclear pore complexes (NPCs) and the spindle pole body (SPB), the yeast equivalent of the centrosome, into the nuclear envelope.

To better understand how Ndc1 completes its diverse tasks, Chen et al. gauged the effects of several mutant versions of the protein. They identified a variant, ndc1-L562S, that was able to attach to components of the NPCs and the SPB. They expected that this mutated protein wouldn’t affect the cells’ survival, but it was lethal because the cells couldn’t replicate the SPB. That finding suggested that Ndc1 might have another binding partner.

The team discovered that Ndc1 normally latches onto a nuclear membrane SUN protein, Mps3, to which ndc1-L562S attached only weakly. Line-scanning fluorescence cross-correlation spectroscopy revealed that the two proteins link up at nuclear membrane locations distinct from NPCs and the SPB. Reducing ndc1-L562S’s association with NPCs increased the protein’s localization to SPBs and rescued the growth of mutant cells. Chen et al. therefore suspect that Mps3 distributes Ndc1 between NPCs and the SPB to ensure that both structures are correctly inserted into the nuclear envelope.